PROJECT ABSTRACT Nearly 2 million people in the United States suffer limb-loss and more than half of them report having phantom limb pain (PLP). The sensations can range from dull to excruciating pain perceived as originating in the missing limb. Although it considerably deteriorates quality of life, the mechanisms and genesis of PLP are not well understood, making it difficult to treat. Spinal cord stimulation (SCS) offers a non-pharmacological option for treating pain and has been shown to be effective in reducing PLP. Aim 1 of the parent grant seeks to produce naturalistic sensations from the missing limb with patterned spinal cord stimulation and assess whether they reduce PLP. Aim 2 of the parent grant seeks to measure and characterize SCS-evoked reflex responses in muscles of the amputated and contralateral limbs. To date, we have found that SCS evokes distinct and localized sensations in the residual and phantom limbs and reflex responses are common. Moreover, the participants involved in these studies have reported a reduction in PLP over the course of the study. We hypothesize that this reduction in pain is due, in part, to a decrease in spinal reflex gain caused by SCS. To test this hypothesis, we propose to measure the ?Hoffmann reflex? and somatosensory evoked potentials to evaluate changes in spinal reflex gain and integrity of the dorsal column sensory pathway, respectively, between the baseline and post-SCS timepoints, and assess their correlations with pain scores.